RNF213 and familial isolated congenital asplenia: The RNF213 genetic variant was identified in 95% of patients with familial MMD, in 80% of patients with sporadic MMD, and in 1.8% of control patients.[16] Recently, Miyawaki and colleagues suggested that a particular subset of Japanese patients with non-MMD intracranial stenosis had a genetic variant associated with MMD.[10,11] In their studies, 22–24% of “ICAS” patients had the RNF213 variant.